/* ----------------------------------------------------------------------
* Copyright (C) 2010-2014 ARM Limited. All rights reserved.
*
* $Date:        19. March 2015
* $Revision: 	V.1.4.5
*
* Project: 	    CMSIS DSP Library
* Title:		arm_conv_fast_q15.c
*
* Description:	Fast Q15 Convolution.
*
* Target Processor: Cortex-M4/Cortex-M3
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
*   - Redistributions of source code must retain the above copyright
*     notice, this list of conditions and the following disclaimer.
*   - Redistributions in binary form must reproduce the above copyright
*     notice, this list of conditions and the following disclaimer in
*     the documentation and/or other materials provided with the
*     distribution.
*   - Neither the name of ARM LIMITED nor the names of its contributors
*     may be used to endorse or promote products derived from this
*     software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
* FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
* COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
* BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
* LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
* CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
* ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
* POSSIBILITY OF SUCH DAMAGE.
* -------------------------------------------------------------------- */

#include "arm_math.h"

/**
 * @ingroup groupFilters
 */

/**
 * @addtogroup Conv
 * @{
 */

/**
 * @brief Convolution of Q15 sequences (fast version) for Cortex-M3 and Cortex-M4.
 * @param[in] *pSrcA points to the first input sequence.
 * @param[in] srcALen length of the first input sequence.
 * @param[in] *pSrcB points to the second input sequence.
 * @param[in] srcBLen length of the second input sequence.
 * @param[out] *pDst points to the location where the output result is written.  Length srcALen+srcBLen-1.
 * @return none.
 *
 * <b>Scaling and Overflow Behavior:</b>
 *
 * \par
 * This fast version uses a 32-bit accumulator with 2.30 format.
 * The accumulator maintains full precision of the intermediate multiplication results
 * but provides only a single guard bit. There is no saturation on intermediate additions.
 * Thus, if the accumulator overflows it wraps around and distorts the result.
 * The input signals should be scaled down to avoid intermediate overflows.
 * Scale down the inputs by log2(min(srcALen, srcBLen)) (log2 is read as log to the base 2) times to avoid overflows,
 * as maximum of min(srcALen, srcBLen) number of additions are carried internally.
 * The 2.30 accumulator is right shifted by 15 bits and then saturated to 1.15 format to yield the final result.
 *
 * \par
 * See <code>arm_conv_q15()</code> for a slower implementation of this function which uses 64-bit accumulation to avoid wrap around distortion.
 */

void arm_conv_fast_q15(
    q15_t *pSrcA,
    uint32_t srcALen,
    q15_t *pSrcB,
    uint32_t srcBLen,
    q15_t *pDst)
{
#ifndef UNALIGNED_SUPPORT_DISABLE
    q15_t *pIn1;                                   /* inputA pointer */
    q15_t *pIn2;                                   /* inputB pointer */
    q15_t *pOut = pDst;                            /* output pointer */
    q31_t sum, acc0, acc1, acc2, acc3;             /* Accumulator */
    q15_t *px;                                     /* Intermediate inputA pointer  */
    q15_t *py;                                     /* Intermediate inputB pointer  */
    q15_t *pSrc1, *pSrc2;                          /* Intermediate pointers */
    q31_t x0, x1, x2, x3, c0;                      /* Temporary variables to hold state and coefficient values */
    uint32_t blockSize1, blockSize2, blockSize3, j, k, count, blkCnt;     /* loop counter */

    /* The algorithm implementation is based on the lengths of the inputs. */
    /* srcB is always made to slide across srcA. */
    /* So srcBLen is always considered as shorter or equal to srcALen */
    if(srcALen >= srcBLen)
    {
        /* Initialization of inputA pointer */
        pIn1 = pSrcA;

        /* Initialization of inputB pointer */
        pIn2 = pSrcB;
    }
    else
    {
        /* Initialization of inputA pointer */
        pIn1 = pSrcB;

        /* Initialization of inputB pointer */
        pIn2 = pSrcA;

        /* srcBLen is always considered as shorter or equal to srcALen */
        j = srcBLen;
        srcBLen = srcALen;
        srcALen = j;
    }

    /* conv(x,y) at n = x[n] * y[0] + x[n-1] * y[1] + x[n-2] * y[2] + ...+ x[n-N+1] * y[N -1] */
    /* The function is internally
     * divided into three stages according to the number of multiplications that has to be
     * taken place between inputA samples and inputB samples. In the first stage of the
     * algorithm, the multiplications increase by one for every iteration.
     * In the second stage of the algorithm, srcBLen number of multiplications are done.
     * In the third stage of the algorithm, the multiplications decrease by one
     * for every iteration. */

    /* The algorithm is implemented in three stages.
       The loop counters of each stage is initiated here. */
    blockSize1 = srcBLen - 1u;
    blockSize2 = srcALen - (srcBLen - 1u);
    blockSize3 = blockSize1;

    /* --------------------------
     * Initializations of stage1
     * -------------------------*/

    /* sum = x[0] * y[0]
     * sum = x[0] * y[1] + x[1] * y[0]
     * ....
     * sum = x[0] * y[srcBlen - 1] + x[1] * y[srcBlen - 2] +...+ x[srcBLen - 1] * y[0]
     */

    /* In this stage the MAC operations are increased by 1 for every iteration.
       The count variable holds the number of MAC operations performed */
    count = 1u;

    /* Working pointer of inputA */
    px = pIn1;

    /* Working pointer of inputB */
    py = pIn2;


    /* ------------------------
     * Stage1 process
     * ----------------------*/

    /* For loop unrolling by 4, this stage is divided into two. */
    /* First part of this stage computes the MAC operations less than 4 */
    /* Second part of this stage computes the MAC operations greater than or equal to 4 */

    /* The first part of the stage starts here */
    while((count < 4u) && (blockSize1 > 0u))
    {
        /* Accumulator is made zero for every iteration */
        sum = 0;

        /* Loop over number of MAC operations between
         * inputA samples and inputB samples */
        k = count;

        while(k > 0u)
        {
            /* Perform the multiply-accumulates */
            sum = __SMLAD(*px++, *py--, sum);

            /* Decrement the loop counter */
            k--;
        }

        /* Store the result in the accumulator in the destination buffer. */
        *pOut++ = (q15_t) (sum >> 15);

        /* Update the inputA and inputB pointers for next MAC calculation */
        py = pIn2 + count;
        px = pIn1;

        /* Increment the MAC count */
        count++;

        /* Decrement the loop counter */
        blockSize1--;
    }

    /* The second part of the stage starts here */
    /* The internal loop, over count, is unrolled by 4 */
    /* To, read the last two inputB samples using SIMD:
     * y[srcBLen] and y[srcBLen-1] coefficients, py is decremented by 1 */
    py = py - 1;

    while(blockSize1 > 0u)
    {
        /* Accumulator is made zero for every iteration */
        sum = 0;

        /* Apply loop unrolling and compute 4 MACs simultaneously. */
        k = count >> 2u;

        /* First part of the processing with loop unrolling.  Compute 4 MACs at a time.
         ** a second loop below computes MACs for the remaining 1 to 3 samples. */
        while(k > 0u)
        {
            /* Perform the multiply-accumulates */
            /* x[0], x[1] are multiplied with y[srcBLen - 1], y[srcBLen - 2] respectively */
            sum = __SMLADX(*__SIMD32(px)++, *__SIMD32(py)--, sum);
            /* x[2], x[3] are multiplied with y[srcBLen - 3], y[srcBLen - 4] respectively */
            sum = __SMLADX(*__SIMD32(px)++, *__SIMD32(py)--, sum);

            /* Decrement the loop counter */
            k--;
        }

        /* For the next MAC operations, the pointer py is used without SIMD
         * So, py is incremented by 1 */
        py = py + 1u;

        /* If the count is not a multiple of 4, compute any remaining MACs here.
         ** No loop unrolling is used. */
        k = count % 0x4u;

        while(k > 0u)
        {
            /* Perform the multiply-accumulates */
            sum = __SMLAD(*px++, *py--, sum);

            /* Decrement the loop counter */
            k--;
        }

        /* Store the result in the accumulator in the destination buffer. */
        *pOut++ = (q15_t) (sum >> 15);

        /* Update the inputA and inputB pointers for next MAC calculation */
        py = pIn2 + (count - 1u);
        px = pIn1;

        /* Increment the MAC count */
        count++;

        /* Decrement the loop counter */
        blockSize1--;
    }

    /* --------------------------
     * Initializations of stage2
     * ------------------------*/

    /* sum = x[0] * y[srcBLen-1] + x[1] * y[srcBLen-2] +...+ x[srcBLen-1] * y[0]
     * sum = x[1] * y[srcBLen-1] + x[2] * y[srcBLen-2] +...+ x[srcBLen] * y[0]
     * ....
     * sum = x[srcALen-srcBLen-2] * y[srcBLen-1] + x[srcALen] * y[srcBLen-2] +...+ x[srcALen-1] * y[0]
     */

    /* Working pointer of inputA */
    px = pIn1;

    /* Working pointer of inputB */
    pSrc2 = pIn2 + (srcBLen - 1u);
    py = pSrc2;

    /* count is the index by which the pointer pIn1 to be incremented */
    count = 0u;


    /* --------------------
     * Stage2 process
     * -------------------*/

    /* Stage2 depends on srcBLen as in this stage srcBLen number of MACS are performed.
     * So, to loop unroll over blockSize2,
     * srcBLen should be greater than or equal to 4 */
    if(srcBLen >= 4u)
    {
        /* Loop unroll over blockSize2, by 4 */
        blkCnt = blockSize2 >> 2u;

        while(blkCnt > 0u)
        {
            py = py - 1u;

            /* Set all accumulators to zero */
            acc0 = 0;
            acc1 = 0;
            acc2 = 0;
            acc3 = 0;


            /* read x[0], x[1] samples */
            x0 = *__SIMD32(px);
            /* read x[1], x[2] samples */
            x1 = _SIMD32_OFFSET(px + 1);
            px += 2u;


            /* Apply loop unrolling and compute 4 MACs simultaneously. */
            k = srcBLen >> 2u;

            /* First part of the processing with loop unrolling.  Compute 4 MACs at a time.
             ** a second loop below computes MACs for the remaining 1 to 3 samples. */
            do
            {
                /* Read the last two inputB samples using SIMD:
                 * y[srcBLen - 1] and y[srcBLen - 2] */
                c0 = *__SIMD32(py)--;

                /* acc0 +=  x[0] * y[srcBLen - 1] + x[1] * y[srcBLen - 2] */
                acc0 = __SMLADX(x0, c0, acc0);

                /* acc1 +=  x[1] * y[srcBLen - 1] + x[2] * y[srcBLen - 2] */
                acc1 = __SMLADX(x1, c0, acc1);

                /* Read x[2], x[3] */
                x2 = *__SIMD32(px);

                /* Read x[3], x[4] */
                x3 = _SIMD32_OFFSET(px + 1);

                /* acc2 +=  x[2] * y[srcBLen - 1] + x[3] * y[srcBLen - 2] */
                acc2 = __SMLADX(x2, c0, acc2);

                /* acc3 +=  x[3] * y[srcBLen - 1] + x[4] * y[srcBLen - 2] */
                acc3 = __SMLADX(x3, c0, acc3);

                /* Read y[srcBLen - 3] and y[srcBLen - 4] */
                c0 = *__SIMD32(py)--;

                /* acc0 +=  x[2] * y[srcBLen - 3] + x[3] * y[srcBLen - 4] */
                acc0 = __SMLADX(x2, c0, acc0);

                /* acc1 +=  x[3] * y[srcBLen - 3] + x[4] * y[srcBLen - 4] */
                acc1 = __SMLADX(x3, c0, acc1);

                /* Read x[4], x[5] */
                x0 = _SIMD32_OFFSET(px + 2);

                /* Read x[5], x[6] */
                x1 = _SIMD32_OFFSET(px + 3);
                px += 4u;

                /* acc2 +=  x[4] * y[srcBLen - 3] + x[5] * y[srcBLen - 4] */
                acc2 = __SMLADX(x0, c0, acc2);

                /* acc3 +=  x[5] * y[srcBLen - 3] + x[6] * y[srcBLen - 4] */
                acc3 = __SMLADX(x1, c0, acc3);

            }
            while(--k);

            /* For the next MAC operations, SIMD is not used
             * So, the 16 bit pointer if inputB, py is updated */

            /* If the srcBLen is not a multiple of 4, compute any remaining MACs here.
             ** No loop unrolling is used. */
            k = srcBLen % 0x4u;

            if(k == 1u)
            {
                /* Read y[srcBLen - 5] */
                c0 = *(py + 1);

#ifdef  ARM_MATH_BIG_ENDIAN

                c0 = c0 << 16u;

#else

                c0 = c0 & 0x0000FFFF;

#endif /*      #ifdef  ARM_MATH_BIG_ENDIAN     */

                /* Read x[7] */
                x3 = *__SIMD32(px);
                px++;

                /* Perform the multiply-accumulates */
                acc0 = __SMLAD(x0, c0, acc0);
                acc1 = __SMLAD(x1, c0, acc1);
                acc2 = __SMLADX(x1, c0, acc2);
                acc3 = __SMLADX(x3, c0, acc3);
            }

            if(k == 2u)
            {
                /* Read y[srcBLen - 5], y[srcBLen - 6] */
                c0 = _SIMD32_OFFSET(py);

                /* Read x[7], x[8] */
                x3 = *__SIMD32(px);

                /* Read x[9] */
                x2 = _SIMD32_OFFSET(px + 1);
                px += 2u;

                /* Perform the multiply-accumulates */
                acc0 = __SMLADX(x0, c0, acc0);
                acc1 = __SMLADX(x1, c0, acc1);
                acc2 = __SMLADX(x3, c0, acc2);
                acc3 = __SMLADX(x2, c0, acc3);
            }

            if(k == 3u)
            {
                /* Read y[srcBLen - 5], y[srcBLen - 6] */
                c0 = _SIMD32_OFFSET(py);

                /* Read x[7], x[8] */
                x3 = *__SIMD32(px);

                /* Read x[9] */
                x2 = _SIMD32_OFFSET(px + 1);

                /* Perform the multiply-accumulates */
                acc0 = __SMLADX(x0, c0, acc0);
                acc1 = __SMLADX(x1, c0, acc1);
                acc2 = __SMLADX(x3, c0, acc2);
                acc3 = __SMLADX(x2, c0, acc3);

                /* Read y[srcBLen - 7] */
                c0 = *(py - 1);
#ifdef  ARM_MATH_BIG_ENDIAN

                c0 = c0 << 16u;
#else

                c0 = c0 & 0x0000FFFF;
#endif /*      #ifdef  ARM_MATH_BIG_ENDIAN     */

                /* Read x[10] */
                x3 =  _SIMD32_OFFSET(px + 2);
                px += 3u;

                /* Perform the multiply-accumulates */
                acc0 = __SMLADX(x1, c0, acc0);
                acc1 = __SMLAD(x2, c0, acc1);
                acc2 = __SMLADX(x2, c0, acc2);
                acc3 = __SMLADX(x3, c0, acc3);
            }

            /* Store the results in the accumulators in the destination buffer. */
#ifndef ARM_MATH_BIG_ENDIAN

            *__SIMD32(pOut)++ = __PKHBT((acc0 >> 15), (acc1 >> 15), 16);
            *__SIMD32(pOut)++ = __PKHBT((acc2 >> 15), (acc3 >> 15), 16);

#else

            *__SIMD32(pOut)++ = __PKHBT((acc1 >> 15), (acc0 >> 15), 16);
            *__SIMD32(pOut)++ = __PKHBT((acc3 >> 15), (acc2 >> 15), 16);

#endif /*      #ifndef  ARM_MATH_BIG_ENDIAN    */

            /* Increment the pointer pIn1 index, count by 4 */
            count += 4u;

            /* Update the inputA and inputB pointers for next MAC calculation */
            px = pIn1 + count;
            py = pSrc2;

            /* Decrement the loop counter */
            blkCnt--;
        }

        /* If the blockSize2 is not a multiple of 4, compute any remaining output samples here.
         ** No loop unrolling is used. */
        blkCnt = blockSize2 % 0x4u;

        while(blkCnt > 0u)
        {
            /* Accumulator is made zero for every iteration */
            sum = 0;

            /* Apply loop unrolling and compute 4 MACs simultaneously. */
            k = srcBLen >> 2u;

            /* First part of the processing with loop unrolling.  Compute 4 MACs at a time.
             ** a second loop below computes MACs for the remaining 1 to 3 samples. */
            while(k > 0u)
            {
                /* Perform the multiply-accumulates */
                sum += ((q31_t) * px++ * *py--);
                sum += ((q31_t) * px++ * *py--);
                sum += ((q31_t) * px++ * *py--);
                sum += ((q31_t) * px++ * *py--);

                /* Decrement the loop counter */
                k--;
            }

            /* If the srcBLen is not a multiple of 4, compute any remaining MACs here.
             ** No loop unrolling is used. */
            k = srcBLen % 0x4u;

            while(k > 0u)
            {
                /* Perform the multiply-accumulates */
                sum += ((q31_t) * px++ * *py--);

                /* Decrement the loop counter */
                k--;
            }

            /* Store the result in the accumulator in the destination buffer. */
            *pOut++ = (q15_t) (sum >> 15);

            /* Increment the pointer pIn1 index, count by 1 */
            count++;

            /* Update the inputA and inputB pointers for next MAC calculation */
            px = pIn1 + count;
            py = pSrc2;

            /* Decrement the loop counter */
            blkCnt--;
        }
    }
    else
    {
        /* If the srcBLen is not a multiple of 4,
         * the blockSize2 loop cannot be unrolled by 4 */
        blkCnt = blockSize2;

        while(blkCnt > 0u)
        {
            /* Accumulator is made zero for every iteration */
            sum = 0;

            /* srcBLen number of MACS should be performed */
            k = srcBLen;

            while(k > 0u)
            {
                /* Perform the multiply-accumulate */
                sum += ((q31_t) * px++ * *py--);

                /* Decrement the loop counter */
                k--;
            }

            /* Store the result in the accumulator in the destination buffer. */
            *pOut++ = (q15_t) (sum >> 15);

            /* Increment the MAC count */
            count++;

            /* Update the inputA and inputB pointers for next MAC calculation */
            px = pIn1 + count;
            py = pSrc2;

            /* Decrement the loop counter */
            blkCnt--;
        }
    }


    /* --------------------------
     * Initializations of stage3
     * -------------------------*/

    /* sum += x[srcALen-srcBLen+1] * y[srcBLen-1] + x[srcALen-srcBLen+2] * y[srcBLen-2] +...+ x[srcALen-1] * y[1]
     * sum += x[srcALen-srcBLen+2] * y[srcBLen-1] + x[srcALen-srcBLen+3] * y[srcBLen-2] +...+ x[srcALen-1] * y[2]
     * ....
     * sum +=  x[srcALen-2] * y[srcBLen-1] + x[srcALen-1] * y[srcBLen-2]
     * sum +=  x[srcALen-1] * y[srcBLen-1]
     */

    /* In this stage the MAC operations are decreased by 1 for every iteration.
       The blockSize3 variable holds the number of MAC operations performed */

    /* Working pointer of inputA */
    pSrc1 = (pIn1 + srcALen) - (srcBLen - 1u);
    px = pSrc1;

    /* Working pointer of inputB */
    pSrc2 = pIn2 + (srcBLen - 1u);
    pIn2 = pSrc2 - 1u;
    py = pIn2;

    /* -------------------
     * Stage3 process
     * ------------------*/

    /* For loop unrolling by 4, this stage is divided into two. */
    /* First part of this stage computes the MAC operations greater than 4 */
    /* Second part of this stage computes the MAC operations less than or equal to 4 */

    /* The first part of the stage starts here */
    j = blockSize3 >> 2u;

    while((j > 0u) && (blockSize3 > 0u))
    {
        /* Accumulator is made zero for every iteration */
        sum = 0;

        /* Apply loop unrolling and compute 4 MACs simultaneously. */
        k = blockSize3 >> 2u;

        /* First part of the processing with loop unrolling.  Compute 4 MACs at a time.
         ** a second loop below computes MACs for the remaining 1 to 3 samples. */
        while(k > 0u)
        {
            /* x[srcALen - srcBLen + 1], x[srcALen - srcBLen + 2] are multiplied
             * with y[srcBLen - 1], y[srcBLen - 2] respectively */
            sum = __SMLADX(*__SIMD32(px)++, *__SIMD32(py)--, sum);
            /* x[srcALen - srcBLen + 3], x[srcALen - srcBLen + 4] are multiplied
             * with y[srcBLen - 3], y[srcBLen - 4] respectively */
            sum = __SMLADX(*__SIMD32(px)++, *__SIMD32(py)--, sum);

            /* Decrement the loop counter */
            k--;
        }

        /* For the next MAC operations, the pointer py is used without SIMD
         * So, py is incremented by 1 */
        py = py + 1u;

        /* If the blockSize3 is not a multiple of 4, compute any remaining MACs here.
         ** No loop unrolling is used. */
        k = blockSize3 % 0x4u;

        while(k > 0u)
        {
            /* sum += x[srcALen - srcBLen + 5] * y[srcBLen - 5] */
            sum = __SMLAD(*px++, *py--, sum);

            /* Decrement the loop counter */
            k--;
        }

        /* Store the result in the accumulator in the destination buffer. */
        *pOut++ = (q15_t) (sum >> 15);

        /* Update the inputA and inputB pointers for next MAC calculation */
        px = ++pSrc1;
        py = pIn2;

        /* Decrement the loop counter */
        blockSize3--;

        j--;
    }

    /* The second part of the stage starts here */
    /* SIMD is not used for the next MAC operations,
     * so pointer py is updated to read only one sample at a time */
    py = py + 1u;

    while(blockSize3 > 0u)
    {
        /* Accumulator is made zero for every iteration */
        sum = 0;

        /* Apply loop unrolling and compute 4 MACs simultaneously. */
        k = blockSize3;

        while(k > 0u)
        {
            /* Perform the multiply-accumulates */
            /* sum +=  x[srcALen-1] * y[srcBLen-1] */
            sum = __SMLAD(*px++, *py--, sum);

            /* Decrement the loop counter */
            k--;
        }

        /* Store the result in the accumulator in the destination buffer. */
        *pOut++ = (q15_t) (sum >> 15);

        /* Update the inputA and inputB pointers for next MAC calculation */
        px = ++pSrc1;
        py = pSrc2;

        /* Decrement the loop counter */
        blockSize3--;
    }

#else
    q15_t *pIn1;                                   /* inputA pointer */
    q15_t *pIn2;                                   /* inputB pointer */
    q15_t *pOut = pDst;                            /* output pointer */
    q31_t sum, acc0, acc1, acc2, acc3;             /* Accumulator */
    q15_t *px;                                     /* Intermediate inputA pointer  */
    q15_t *py;                                     /* Intermediate inputB pointer  */
    q15_t *pSrc1, *pSrc2;                          /* Intermediate pointers */
    q31_t x0, x1, x2, x3, c0;                      /* Temporary variables to hold state and coefficient values */
    uint32_t blockSize1, blockSize2, blockSize3, j, k, count, blkCnt;     /* loop counter */
    q15_t a, b;

    /* The algorithm implementation is based on the lengths of the inputs. */
    /* srcB is always made to slide across srcA. */
    /* So srcBLen is always considered as shorter or equal to srcALen */
    if(srcALen >= srcBLen)
    {
        /* Initialization of inputA pointer */
        pIn1 = pSrcA;

        /* Initialization of inputB pointer */
        pIn2 = pSrcB;
    }
    else
    {
        /* Initialization of inputA pointer */
        pIn1 = pSrcB;

        /* Initialization of inputB pointer */
        pIn2 = pSrcA;

        /* srcBLen is always considered as shorter or equal to srcALen */
        j = srcBLen;
        srcBLen = srcALen;
        srcALen = j;
    }

    /* conv(x,y) at n = x[n] * y[0] + x[n-1] * y[1] + x[n-2] * y[2] + ...+ x[n-N+1] * y[N -1] */
    /* The function is internally
     * divided into three stages according to the number of multiplications that has to be
     * taken place between inputA samples and inputB samples. In the first stage of the
     * algorithm, the multiplications increase by one for every iteration.
     * In the second stage of the algorithm, srcBLen number of multiplications are done.
     * In the third stage of the algorithm, the multiplications decrease by one
     * for every iteration. */

    /* The algorithm is implemented in three stages.
       The loop counters of each stage is initiated here. */
    blockSize1 = srcBLen - 1u;
    blockSize2 = srcALen - (srcBLen - 1u);
    blockSize3 = blockSize1;

    /* --------------------------
     * Initializations of stage1
     * -------------------------*/

    /* sum = x[0] * y[0]
     * sum = x[0] * y[1] + x[1] * y[0]
     * ....
     * sum = x[0] * y[srcBlen - 1] + x[1] * y[srcBlen - 2] +...+ x[srcBLen - 1] * y[0]
     */

    /* In this stage the MAC operations are increased by 1 for every iteration.
       The count variable holds the number of MAC operations performed */
    count = 1u;

    /* Working pointer of inputA */
    px = pIn1;

    /* Working pointer of inputB */
    py = pIn2;


    /* ------------------------
     * Stage1 process
     * ----------------------*/

    /* For loop unrolling by 4, this stage is divided into two. */
    /* First part of this stage computes the MAC operations less than 4 */
    /* Second part of this stage computes the MAC operations greater than or equal to 4 */

    /* The first part of the stage starts here */
    while((count < 4u) && (blockSize1 > 0u))
    {
        /* Accumulator is made zero for every iteration */
        sum = 0;

        /* Loop over number of MAC operations between
         * inputA samples and inputB samples */
        k = count;

        while(k > 0u)
        {
            /* Perform the multiply-accumulates */
            sum += ((q31_t) * px++ * *py--);

            /* Decrement the loop counter */
            k--;
        }

        /* Store the result in the accumulator in the destination buffer. */
        *pOut++ = (q15_t) (sum >> 15);

        /* Update the inputA and inputB pointers for next MAC calculation */
        py = pIn2 + count;
        px = pIn1;

        /* Increment the MAC count */
        count++;

        /* Decrement the loop counter */
        blockSize1--;
    }

    /* The second part of the stage starts here */
    /* The internal loop, over count, is unrolled by 4 */
    /* To, read the last two inputB samples using SIMD:
     * y[srcBLen] and y[srcBLen-1] coefficients, py is decremented by 1 */
    py = py - 1;

    while(blockSize1 > 0u)
    {
        /* Accumulator is made zero for every iteration */
        sum = 0;

        /* Apply loop unrolling and compute 4 MACs simultaneously. */
        k = count >> 2u;

        /* First part of the processing with loop unrolling.  Compute 4 MACs at a time.
         ** a second loop below computes MACs for the remaining 1 to 3 samples. */
        py++;

        while(k > 0u)
        {
            /* Perform the multiply-accumulates */
            sum += ((q31_t) * px++ * *py--);
            sum += ((q31_t) * px++ * *py--);
            sum += ((q31_t) * px++ * *py--);
            sum += ((q31_t) * px++ * *py--);

            /* Decrement the loop counter */
            k--;
        }

        /* If the count is not a multiple of 4, compute any remaining MACs here.
         ** No loop unrolling is used. */
        k = count % 0x4u;

        while(k > 0u)
        {
            /* Perform the multiply-accumulates */
            sum += ((q31_t) * px++ * *py--);

            /* Decrement the loop counter */
            k--;
        }

        /* Store the result in the accumulator in the destination buffer. */
        *pOut++ = (q15_t) (sum >> 15);

        /* Update the inputA and inputB pointers for next MAC calculation */
        py = pIn2 + (count - 1u);
        px = pIn1;

        /* Increment the MAC count */
        count++;

        /* Decrement the loop counter */
        blockSize1--;
    }

    /* --------------------------
     * Initializations of stage2
     * ------------------------*/

    /* sum = x[0] * y[srcBLen-1] + x[1] * y[srcBLen-2] +...+ x[srcBLen-1] * y[0]
     * sum = x[1] * y[srcBLen-1] + x[2] * y[srcBLen-2] +...+ x[srcBLen] * y[0]
     * ....
     * sum = x[srcALen-srcBLen-2] * y[srcBLen-1] + x[srcALen] * y[srcBLen-2] +...+ x[srcALen-1] * y[0]
     */

    /* Working pointer of inputA */
    px = pIn1;

    /* Working pointer of inputB */
    pSrc2 = pIn2 + (srcBLen - 1u);
    py = pSrc2;

    /* count is the index by which the pointer pIn1 to be incremented */
    count = 0u;


    /* --------------------
     * Stage2 process
     * -------------------*/

    /* Stage2 depends on srcBLen as in this stage srcBLen number of MACS are performed.
     * So, to loop unroll over blockSize2,
     * srcBLen should be greater than or equal to 4 */
    if(srcBLen >= 4u)
    {
        /* Loop unroll over blockSize2, by 4 */
        blkCnt = blockSize2 >> 2u;

        while(blkCnt > 0u)
        {
            py = py - 1u;

            /* Set all accumulators to zero */
            acc0 = 0;
            acc1 = 0;
            acc2 = 0;
            acc3 = 0;

            /* read x[0], x[1] samples */
            a = *px++;
            b = *px++;

#ifndef ARM_MATH_BIG_ENDIAN

            x0 = __PKHBT(a, b, 16);
            a = *px;
            x1 = __PKHBT(b, a, 16);

#else

            x0 = __PKHBT(b, a, 16);
            a = *px;
            x1 = __PKHBT(a, b, 16);

#endif	/*	#ifndef ARM_MATH_BIG_ENDIAN	   */

            /* Apply loop unrolling and compute 4 MACs simultaneously. */
            k = srcBLen >> 2u;

            /* First part of the processing with loop unrolling.  Compute 4 MACs at a time.
             ** a second loop below computes MACs for the remaining 1 to 3 samples. */
            do
            {
                /* Read the last two inputB samples using SIMD:
                 * y[srcBLen - 1] and y[srcBLen - 2] */
                a = *py;
                b = *(py + 1);
                py -= 2;

#ifndef ARM_MATH_BIG_ENDIAN

                c0 = __PKHBT(a, b, 16);

#else

                c0 = __PKHBT(b, a, 16);;

#endif	/*	#ifndef ARM_MATH_BIG_ENDIAN	*/

                /* acc0 +=  x[0] * y[srcBLen - 1] + x[1] * y[srcBLen - 2] */
                acc0 = __SMLADX(x0, c0, acc0);

                /* acc1 +=  x[1] * y[srcBLen - 1] + x[2] * y[srcBLen - 2] */
                acc1 = __SMLADX(x1, c0, acc1);

                a = *px;
                b = *(px + 1);

#ifndef ARM_MATH_BIG_ENDIAN

                x2 = __PKHBT(a, b, 16);
                a = *(px + 2);
                x3 = __PKHBT(b, a, 16);

#else

                x2 = __PKHBT(b, a, 16);
                a = *(px + 2);
                x3 = __PKHBT(a, b, 16);

#endif	/*	#ifndef ARM_MATH_BIG_ENDIAN	   */

                /* acc2 +=  x[2] * y[srcBLen - 1] + x[3] * y[srcBLen - 2] */
                acc2 = __SMLADX(x2, c0, acc2);

                /* acc3 +=  x[3] * y[srcBLen - 1] + x[4] * y[srcBLen - 2] */
                acc3 = __SMLADX(x3, c0, acc3);

                /* Read y[srcBLen - 3] and y[srcBLen - 4] */
                a = *py;
                b = *(py + 1);
                py -= 2;

#ifndef ARM_MATH_BIG_ENDIAN

                c0 = __PKHBT(a, b, 16);

#else

                c0 = __PKHBT(b, a, 16);;

#endif	/*	#ifndef ARM_MATH_BIG_ENDIAN	*/

                /* acc0 +=  x[2] * y[srcBLen - 3] + x[3] * y[srcBLen - 4] */
                acc0 = __SMLADX(x2, c0, acc0);

                /* acc1 +=  x[3] * y[srcBLen - 3] + x[4] * y[srcBLen - 4] */
                acc1 = __SMLADX(x3, c0, acc1);

                /* Read x[4], x[5], x[6] */
                a = *(px + 2);
                b = *(px + 3);

#ifndef ARM_MATH_BIG_ENDIAN

                x0 = __PKHBT(a, b, 16);
                a = *(px + 4);
                x1 = __PKHBT(b, a, 16);

#else

                x0 = __PKHBT(b, a, 16);
                a = *(px + 4);
                x1 = __PKHBT(a, b, 16);

#endif	/*	#ifndef ARM_MATH_BIG_ENDIAN	   */

                px += 4u;

                /* acc2 +=  x[4] * y[srcBLen - 3] + x[5] * y[srcBLen - 4] */
                acc2 = __SMLADX(x0, c0, acc2);

                /* acc3 +=  x[5] * y[srcBLen - 3] + x[6] * y[srcBLen - 4] */
                acc3 = __SMLADX(x1, c0, acc3);

            }
            while(--k);

            /* For the next MAC operations, SIMD is not used
             * So, the 16 bit pointer if inputB, py is updated */

            /* If the srcBLen is not a multiple of 4, compute any remaining MACs here.
             ** No loop unrolling is used. */
            k = srcBLen % 0x4u;

            if(k == 1u)
            {
                /* Read y[srcBLen - 5] */
                c0 = *(py + 1);

#ifdef  ARM_MATH_BIG_ENDIAN

                c0 = c0 << 16u;

#else

                c0 = c0 & 0x0000FFFF;

#endif /*      #ifdef  ARM_MATH_BIG_ENDIAN     */

                /* Read x[7] */
                a = *px;
                b = *(px + 1);
                px++;

#ifndef ARM_MATH_BIG_ENDIAN

                x3 = __PKHBT(a, b, 16);

#else

                x3 = __PKHBT(b, a, 16);;

#endif	/*	#ifndef ARM_MATH_BIG_ENDIAN	*/


                /* Perform the multiply-accumulates */
                acc0 = __SMLAD(x0, c0, acc0);
                acc1 = __SMLAD(x1, c0, acc1);
                acc2 = __SMLADX(x1, c0, acc2);
                acc3 = __SMLADX(x3, c0, acc3);
            }

            if(k == 2u)
            {
                /* Read y[srcBLen - 5], y[srcBLen - 6] */
                a = *py;
                b = *(py + 1);

#ifndef ARM_MATH_BIG_ENDIAN

                c0 = __PKHBT(a, b, 16);

#else

                c0 = __PKHBT(b, a, 16);;

#endif	/*	#ifndef ARM_MATH_BIG_ENDIAN	*/

                /* Read x[7], x[8], x[9] */
                a = *px;
                b = *(px + 1);

#ifndef ARM_MATH_BIG_ENDIAN

                x3 = __PKHBT(a, b, 16);
                a = *(px + 2);
                x2 = __PKHBT(b, a, 16);

#else

                x3 = __PKHBT(b, a, 16);
                a = *(px + 2);
                x2 = __PKHBT(a, b, 16);

#endif	/*	#ifndef ARM_MATH_BIG_ENDIAN	   */
                px += 2u;

                /* Perform the multiply-accumulates */
                acc0 = __SMLADX(x0, c0, acc0);
                acc1 = __SMLADX(x1, c0, acc1);
                acc2 = __SMLADX(x3, c0, acc2);
                acc3 = __SMLADX(x2, c0, acc3);
            }

            if(k == 3u)
            {
                /* Read y[srcBLen - 5], y[srcBLen - 6] */
                a = *py;
                b = *(py + 1);

#ifndef ARM_MATH_BIG_ENDIAN

                c0 = __PKHBT(a, b, 16);

#else

                c0 = __PKHBT(b, a, 16);;

#endif	/*	#ifndef ARM_MATH_BIG_ENDIAN	*/

                /* Read x[7], x[8], x[9] */
                a = *px;
                b = *(px + 1);

#ifndef ARM_MATH_BIG_ENDIAN

                x3 = __PKHBT(a, b, 16);
                a = *(px + 2);
                x2 = __PKHBT(b, a, 16);

#else

                x3 = __PKHBT(b, a, 16);
                a = *(px + 2);
                x2 = __PKHBT(a, b, 16);

#endif	/*	#ifndef ARM_MATH_BIG_ENDIAN	   */

                /* Perform the multiply-accumulates */
                acc0 = __SMLADX(x0, c0, acc0);
                acc1 = __SMLADX(x1, c0, acc1);
                acc2 = __SMLADX(x3, c0, acc2);
                acc3 = __SMLADX(x2, c0, acc3);

                /* Read y[srcBLen - 7] */
                c0 = *(py - 1);
#ifdef  ARM_MATH_BIG_ENDIAN

                c0 = c0 << 16u;
#else

                c0 = c0 & 0x0000FFFF;
#endif /*      #ifdef  ARM_MATH_BIG_ENDIAN     */

                /* Read x[10] */
                a = *(px + 2);
                b = *(px + 3);

#ifndef ARM_MATH_BIG_ENDIAN

                x3 = __PKHBT(a, b, 16);

#else

                x3 = __PKHBT(b, a, 16);;

#endif	/*	#ifndef ARM_MATH_BIG_ENDIAN	*/

                px += 3u;

                /* Perform the multiply-accumulates */
                acc0 = __SMLADX(x1, c0, acc0);
                acc1 = __SMLAD(x2, c0, acc1);
                acc2 = __SMLADX(x2, c0, acc2);
                acc3 = __SMLADX(x3, c0, acc3);
            }

            /* Store the results in the accumulators in the destination buffer. */
            *pOut++ = (q15_t)(acc0 >> 15);
            *pOut++ = (q15_t)(acc1 >> 15);
            *pOut++ = (q15_t)(acc2 >> 15);
            *pOut++ = (q15_t)(acc3 >> 15);

            /* Increment the pointer pIn1 index, count by 4 */
            count += 4u;

            /* Update the inputA and inputB pointers for next MAC calculation */
            px = pIn1 + count;
            py = pSrc2;

            /* Decrement the loop counter */
            blkCnt--;
        }

        /* If the blockSize2 is not a multiple of 4, compute any remaining output samples here.
         ** No loop unrolling is used. */
        blkCnt = blockSize2 % 0x4u;

        while(blkCnt > 0u)
        {
            /* Accumulator is made zero for every iteration */
            sum = 0;

            /* Apply loop unrolling and compute 4 MACs simultaneously. */
            k = srcBLen >> 2u;

            /* First part of the processing with loop unrolling.  Compute 4 MACs at a time.
             ** a second loop below computes MACs for the remaining 1 to 3 samples. */
            while(k > 0u)
            {
                /* Perform the multiply-accumulates */
                sum += ((q31_t) * px++ * *py--);
                sum += ((q31_t) * px++ * *py--);
                sum += ((q31_t) * px++ * *py--);
                sum += ((q31_t) * px++ * *py--);

                /* Decrement the loop counter */
                k--;
            }

            /* If the srcBLen is not a multiple of 4, compute any remaining MACs here.
             ** No loop unrolling is used. */
            k = srcBLen % 0x4u;

            while(k > 0u)
            {
                /* Perform the multiply-accumulates */
                sum += ((q31_t) * px++ * *py--);

                /* Decrement the loop counter */
                k--;
            }

            /* Store the result in the accumulator in the destination buffer. */
            *pOut++ = (q15_t) (sum >> 15);

            /* Increment the pointer pIn1 index, count by 1 */
            count++;

            /* Update the inputA and inputB pointers for next MAC calculation */
            px = pIn1 + count;
            py = pSrc2;

            /* Decrement the loop counter */
            blkCnt--;
        }
    }
    else
    {
        /* If the srcBLen is not a multiple of 4,
         * the blockSize2 loop cannot be unrolled by 4 */
        blkCnt = blockSize2;

        while(blkCnt > 0u)
        {
            /* Accumulator is made zero for every iteration */
            sum = 0;

            /* srcBLen number of MACS should be performed */
            k = srcBLen;

            while(k > 0u)
            {
                /* Perform the multiply-accumulate */
                sum += ((q31_t) * px++ * *py--);

                /* Decrement the loop counter */
                k--;
            }

            /* Store the result in the accumulator in the destination buffer. */
            *pOut++ = (q15_t) (sum >> 15);

            /* Increment the MAC count */
            count++;

            /* Update the inputA and inputB pointers for next MAC calculation */
            px = pIn1 + count;
            py = pSrc2;

            /* Decrement the loop counter */
            blkCnt--;
        }
    }


    /* --------------------------
     * Initializations of stage3
     * -------------------------*/

    /* sum += x[srcALen-srcBLen+1] * y[srcBLen-1] + x[srcALen-srcBLen+2] * y[srcBLen-2] +...+ x[srcALen-1] * y[1]
     * sum += x[srcALen-srcBLen+2] * y[srcBLen-1] + x[srcALen-srcBLen+3] * y[srcBLen-2] +...+ x[srcALen-1] * y[2]
     * ....
     * sum +=  x[srcALen-2] * y[srcBLen-1] + x[srcALen-1] * y[srcBLen-2]
     * sum +=  x[srcALen-1] * y[srcBLen-1]
     */

    /* In this stage the MAC operations are decreased by 1 for every iteration.
       The blockSize3 variable holds the number of MAC operations performed */

    /* Working pointer of inputA */
    pSrc1 = (pIn1 + srcALen) - (srcBLen - 1u);
    px = pSrc1;

    /* Working pointer of inputB */
    pSrc2 = pIn2 + (srcBLen - 1u);
    pIn2 = pSrc2 - 1u;
    py = pIn2;

    /* -------------------
     * Stage3 process
     * ------------------*/

    /* For loop unrolling by 4, this stage is divided into two. */
    /* First part of this stage computes the MAC operations greater than 4 */
    /* Second part of this stage computes the MAC operations less than or equal to 4 */

    /* The first part of the stage starts here */
    j = blockSize3 >> 2u;

    while((j > 0u) && (blockSize3 > 0u))
    {
        /* Accumulator is made zero for every iteration */
        sum = 0;

        /* Apply loop unrolling and compute 4 MACs simultaneously. */
        k = blockSize3 >> 2u;

        /* First part of the processing with loop unrolling.  Compute 4 MACs at a time.
         ** a second loop below computes MACs for the remaining 1 to 3 samples. */
        py++;

        while(k > 0u)
        {
            sum += ((q31_t) * px++ * *py--);
            sum += ((q31_t) * px++ * *py--);
            sum += ((q31_t) * px++ * *py--);
            sum += ((q31_t) * px++ * *py--);
            /* Decrement the loop counter */
            k--;
        }

        /* If the blockSize3 is not a multiple of 4, compute any remaining MACs here.
         ** No loop unrolling is used. */
        k = blockSize3 % 0x4u;

        while(k > 0u)
        {
            /* sum += x[srcALen - srcBLen + 5] * y[srcBLen - 5] */
            sum += ((q31_t) * px++ * *py--);

            /* Decrement the loop counter */
            k--;
        }

        /* Store the result in the accumulator in the destination buffer. */
        *pOut++ = (q15_t) (sum >> 15);

        /* Update the inputA and inputB pointers for next MAC calculation */
        px = ++pSrc1;
        py = pIn2;

        /* Decrement the loop counter */
        blockSize3--;

        j--;
    }

    /* The second part of the stage starts here */
    /* SIMD is not used for the next MAC operations,
     * so pointer py is updated to read only one sample at a time */
    py = py + 1u;

    while(blockSize3 > 0u)
    {
        /* Accumulator is made zero for every iteration */
        sum = 0;

        /* Apply loop unrolling and compute 4 MACs simultaneously. */
        k = blockSize3;

        while(k > 0u)
        {
            /* Perform the multiply-accumulates */
            /* sum +=  x[srcALen-1] * y[srcBLen-1] */
            sum += ((q31_t) * px++ * *py--);

            /* Decrement the loop counter */
            k--;
        }

        /* Store the result in the accumulator in the destination buffer. */
        *pOut++ = (q15_t) (sum >> 15);

        /* Update the inputA and inputB pointers for next MAC calculation */
        px = ++pSrc1;
        py = pSrc2;

        /* Decrement the loop counter */
        blockSize3--;
    }

#endif	/*	#ifndef UNALIGNED_SUPPORT_DISABLE	*/
}

/**
 * @} end of Conv group
 */
